Photographic masking using the clayden effect



.J. A. c. YULE 2,444,867

PHOTOGRAPHIC MASKING USING THE CLAYDEN EFFECT Filed July 26, 1945 July 6, 1948.

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?atentecl July 6, i948 PHOTOGRAPHIC MASKING USING THE CLAYDEN EFFECT John A. C. Yule, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application July 26, 1945, Serial No. 607,211

7 Claims. (01. 95-2) This invention relates to photography and particularly to a method of producing masked photographic images.

For the color correction of photographic or photo-mechanical color reproductions or for improving the rendering of fine detail, a masking method is often used. This consists of the combination of a negative and a positive in register with each other. Whichever of these images has the lower contrast is known as the mask. For example, a low contrast red filter positive mask may be combined with a green filter negative to produce a corrected green filter negative. It is generally necessary to make a separate low contrast masking image either negative or positive, depending upon whether a positive or negative image is to be masked and this of course requires additional steps and additional photographic material. In Seymour U. S. Patent 2,169,009, granted August 8, 1939, the final positive relief images are used as masks but in other processes a separate masking image must be made. It is therefore an object of the present invention to provide a simplified method of masking.

A further object is to provide a method which silver halide layer under an image, toa high intensity light source for a short period of time, and exposing the layer under a different image for a longer period of time to a low intensity light source. The high intensity light desensitizes the layer so that a reduction in density is obtained in the portions so exposed.

In the accompanying drawing, the ingle figure is a diagram of the method of making corrected color separation images according to my invention.

The presentinvention makes use of the Clayden effect, which is a photographic efiect discovered by Clayden in 1899 in connection with photographic exposures to lightning flashes. The feature which characterizes the Clayden effect is the initial exposure to high intensity light which desensitizes the emulsion so that subsequent exposure to low intensity light produces less efiect than if the pre-exposure had not been given.

According to my invention a silver halide photographic layer is exposed to a very intense image which will be called the masking image, for .a very short time. This exposure may be made in the camera using a colored filter so that a color separation image is obtained or it may be made in a printer using a color separation image on a photographic film or plate. The silver halide layer is then again exposed in register for a longer period of time to a second low intensity image, which will be called the main image, of the same subject at the same magnification. The silver halide layer is then developed, preferably in a high contrast developer, to obtain a corrected color separation image of the main image.

In my process, the masking image and the main image may be considered to be positive with respect to each other, although the effect of the masking image is negative, since its action is reversed by means of the Clayden effect. The value of the method depends upon the fact that it permits the use of images which are positive with respect to each other. By positive with respect to each other I mean that the masking image and the main image are both positive or are both negatives. Generally, in masking processes, as stated above, the masking image is negative with respect to the main image, that is, a positive masking image is used to mask a negative main image or vice versa, and this is the reason thatthe positives or negatives already available are unsuitable for masks.

The masking of desensitizing exposures used in my method must be of high intensity and short duration. The desensitizing exposure should be less than 0.001 second, preferably less than 0.0002 second. An exposure of this order is obtained with the Kodatron speed lamp, studio type, which produces a light intensity of about 12,000 lumens and has a flash time of approximately 0.0001 second. Owing to the extreme variation in exposures required to produce the Clayden effect with different emulsions, it is not possible to give the light intensity in exposure terms. However, the desensitizing exposure should be not less than four times and not more than 1000 times the Clayden threshold value. The Clayden threshold value is the least exposure required to cause a visible decrease in the density produced by a lsubsequent normal (low intensity) exposure.

My process will be described in greater details by reference to the following example for the preparation of a corrected color separation image.

In the drawings, a color transparency is hown consisting of a transparent base I0 having thereon superposed layers containing cyan, magenta and yellow images ll, l2 and [3,.respectiVe1y,

To make a color corrected green filter negative, a photographic film l6 such as Kodak Tri-X panchromatic sheet film is first exposed through the transparency with a red filter l4 and a high intensity light of short duration such as that from the Kodatron speed lamp. This is the masking exposure and partially desensitizes 1 portions I! and IBof the emulsion layer offilm l6 but'has no efiect on portion 19 which is produced by the cyan image H. An exposure is then made through a green filter IS with a-low intensity:

light such as 1 meter-candle of light for"10sec-" onds. After development in a non-solvent (low sulfite) developer such as 1 part of'Kodak D-'7 2-'-- developer diluted with 3 parts of'water'," portion" [13 has a low density because it was desensitized by the first exposure and protected by the ma genta layer [2 from the second exposure. Portion l9 develops to a medium density since it partially protected by the green absorption of the cyan dye. If it had' not received-the desensitizin'g' 'exposure, portion lT'wo'uld have developed te-- a'- higher density than portion-10 However,

'tl'ieefiect ofthe de'sensitizing exposure is to reduce the density of portion l'l until-it is approximately-equal to that of portion l9,thus compensating-for the undesired absorption of the cyan dy'e.--

Apple! corrected blue filter negative may similarly' 'be given a-short -high intensity exposure through the greenfilterfollowed by a low intensity exposure through the blue fllter.

My method'can also'beused in the preparatien -of un'sharp masks for preserving detail'in line Work-as described'in my priorapplication, Serif-No; 438,633; filed April 11,' 1942; now Patent Noi"2,420,636,"of May 13,1947. According to 'method the camera is thrown-'slightlyout of focus and-a short'desensitizing' exposure is made witlr'th'e 'Ko'datron lamp; This out-of-focus image isithe masking image. The camerais th'enro-cused accurately; care being takennot'to change? the size of the image, and the: main "exosureis made; The local desensitizing"action oftlieifirst exposure" prevents 'the fine details from b'ir'ig' overexposed and yet permits the rest of thesubject to be given full exposure;

In my masking 'method, thecontr'as't of the mask image depends upon the type of film, that is'}'.t1i method by Which the emulsion is made, tl'i'e'Tdifelo'per, and the" duration'andintensity ofw thetwo'exposures.

As.- stated above, by high intensity light, I mean light giving an exposure of not less than four; times nor more than 1'0'00'tii'nes the CIa'yden efict'threshold value (as defined above) of the emulsion :at that particular exposure time which is us'ed'lf. By low intensity light, I mean light whichisT-of 'such low intensity that" it does not producea Clayden effect (i. e. hasnodesensiti'zinglactionl however prolongedthe exposure may be. The highintensity lightis usedfor a period not-exceeding 0.001 second and the low intensity light" is" used for a time longer than 0.0001

second.

By. .fi'mmediately exposing the emulsion .to low int'ensitylight after the Clayden efiect exposure, I'Iiiiean'tliat there is no intermediate treatment, such 'as. development, between the exposures. Tneseeond exposure need not be immediate with respect to time. p

Itiwill be understood that the modifications andiexamples described herein are" illustrative onlyiand that myi invention is who take'nas limite'd only by the scopeof the appended'claimsf I claim:

1. The method of photographic masking, which comprises exposing a silver halide emulsion layer to an image of a subject for a period not exceeding 0.001 second, with a high intensity light beam producing an exposure of from 4 to 1000 times the Clayden thresholdvalue of the emulsion; and thereby desensitizingthe exposed portions of the layer, then exposing said layer *to a second image of the same subject with a low intensity light-source having no desensitizing acti01'1,"f01 a longer time than 0.001 second to produce a developable image, and developing the emulsion with a silver halide developing agent.

2.: Themethod'of photographic masking which comprises exposing a silver halide emulsion layer toacol'or separation image of a subject for a periodnot exceeding 0.001 second, with a high intensity light beam producing an exposure of from 4. to 1000 times the Clayden threshold value of the emu-1sion-,- and thereby desensitizin'g -the exposed portions of 'thelayer, then immediately exposing said layer to a diiferent'color separation image of said subject, with-a-low intensity-light source having no desensitizingaction for-a'longer time than 0.001 second to produce'a-developable image and developing the emulsion with a silver halide developing agent.

3. The method of photographic mask i ng which comprises exposing a silver halide' emulsio'n' laye'r to -a red filter separation image of a 'subiect for a periodnot exceeding 0.001 second', -witlia high intensity light beam producing:an-exposure-of from 4 to 1000 times the Clayden threshold value of the emulsion and thereby-desensitizin'g-gthe exposed portions of the layer;- then immediately exposing said layer to a greenfilterseparation image ofsaid-subject; with a low intensity lig-ht source having nodese'nsitizing action for a longer time -than-0.001 second to produce a developable image, and developing the emulsion with asilver halide developing agent.-

4. Themethod ofphotog'raphic'masking which comprises exposing asilve'r halide emulsion layer to a colorseparation image of a-sub'ject-iora period of approximately 0.0001 second, with a high intensity light beam producing an exposure of'from etc 1000 times theClayden-threshold value of the emulsion,- and thereby desensitizing theexposed portions of-the layer, then immediately' exposing said layer to a difierenflcolor separation image of saidsubject with a lowintensity light source having no desensltizing ac tion for-alonger time than-0.001second-to 'produce a developable image-and developin -=the emulsion with-asilv'er halide developing "agent.

5. The method of photographicinaskingwhich comprises exposing-a silver halide-emulsion layer to an image of a'subject and' sl-ightly-'out'of focus with said image for a period-of time not-exceeding 0.001 second with a high intensity light beam of from 4 to 1000 timesthe Glayden threshold-value' of the emulsion; and thereby desensititing the exposed portions of the -layer;-then* exposing said layer-to saidimage andin fo'cus-with-"said image atthe same magnification asin theformer exposure, with a low intensity light source having no 'desensitizing' action for: a longer time than 0.001 second 'to produce a *d'evelopable im'age an'd developing the emulsion with a-silver halidedewith said image ior'a'period of'time of *approxb mately 0.0001 second, with a high intensity light beam of from 4 to 1000 times the Clayden threshold value of the emulsion, and thereby desensitizing the exposed portions of the layer, then exposing said layer to said image and in focus with said image at the same magnification as in the former exposure, with a low intensity light source having no desensitizing action for a longer time than 0.001 second to produce a developable image, and developing the emulsion with a silver, halide developing agent.

7. The method of photographic masking, which comprises exposing a silver halide emulsion layer to a green filter separation image of a subject for a period not exceeding 0.001 second, with a high intensity light beam of from 4 to 1000 times the Clayden threshold value of the emulsion, and

REFERENCES CITED The following references are of record in the file of this patent:

Mees: The Theory of the Photographic Process, The Macmillan 00., N. Y., 1942; pages 168, 196, 254, 255', 256, 257 and 260. (Copy in Division 7.) 

